Me and Charlotte
You're the same age, come from the same place, have the sames tastes and even similar luck with men...Charlotte is your double. You see yourself in her in so many ways that it's like looking in a mirror when you look at her. Even on a physical level, no-one else could be mistaken for her apart from you: you're on an equal footing. You get on well together because she resembles you and understands you. You share everything: your ups, your downs and your hangovers.
But watch out for...
The problem with this type of friendship is that it can soon get competitive. If Charlotte has a new boyfriend but you're single, you'll want to find a funnier, better-looking specimen. If you get promoted at work, she might end up wanting to change jobs. This is because success for one is experience as failure for the other. This desire for equality can take its toll on your friendship.
How can I optimise our friendship?
Unglue yourselves! You don't need to spend every minute of your lives together. Take a more independent approach to life so that you stop comparing yourselves to each other all the time. Of course, you can still see each other regularly and have fun together, but have other friends as well and do things with them or on your own.
Your friendship will benefit from a bit of freedom, without which no relationship can survive.